Degumming of bast fibres

ABSTRACT

A method for separating decorticated bast skin into individual fibres, comprising maintaining decorticated bast skin in a closed container in the presence of at least one enzymatic and/or chemical retting agent for a period sufficient for at least a portion of the fibre bundles to separate into individual fibres.

TECHNICAL FIELD

[0001] This invention concerns a method for producing bast fibres,particularly hemp fibres. The invention also extends to bast fibresproduced by the method of the present invention and to yams, fabrics andmaterials manufactured from these fibres. The invention further providesa method for the evaluation of the quality of degummed bast fibres.

BACKGROUND

[0002] Traditionally, plant bast fibres have been degummed by retting. Anumber of retting techniques have been developed - dew retting, poolretting, stream retting, tank retting, chemical retting, enzymaticretting, and/or a combination of these techniques.

[0003] Dew retting is a process in which the fibres (eg flax) aretreated by exposure in the field to the action of dew and sunlight. Itis labour intensive, takes several weeks and the retted fibres areusually inconsistent in quality.

[0004] Pool retting is the most rapid of the existing natural rettingtechniques because of the excess bacteria in stagnant water which speedsup fermentation. This technique takes about a week.

[0005] Stream retting is similar to pool retting, except the bast fibres(eg flax) are placed in a flowing stream that does not have as much ofthe bacteria that is required for good retting. Clearly, this techniquerequires that a stream be located nearby.

[0006] Tank retting is considered to be the best and the quickest methodof retting, taking only about 3 days. Finer fibre results from thismethod.

[0007] Chemical retting relies on the action of chemicals such as sodaash, caustic soda and oxalic acid and the action can be violent anduncontrollable, if the retting process is not carried out properly.While chemical retting has been carried out on an industrial scale,further improvement in the retting process is a subject of on-goingresearch.

[0008] Enzymatic retting of bast fibres has been reported before, usingvarious procedures that give fibres of different quality attributes.

[0009] The quest for new and improved ways of degumming is ongoing. Wehave discovered that degumming of fibre bundles in decorticated bastfibre can be achieved by enzymatic and/or chemical retting of thedecorticated fibre in a closed, substantially gas impermeable container,for example, a plastic bag. An advantage of carrying out refting in aclosed container is that the fibres are protected from otherenvironmental factors that may lead to unwanted degradation of thefibre. A further advantage in the case of enzymatic retting is that itallows the action of the enzyme to be carried under anaerobicconditions. In addition, this technique has the potential ofsignificantly reducing water consumption compared to traditional rettingmethods.

SUMMARY OF THE INVENTION

[0010] Accordingly, in a first aspect, the present invention provides amethod for separating bast skin into individual fibres, comprisingmaintaining bast skin in a closed container in the presence of at leastone enzymatic and/or chemical retting agent for a period sufficient forat least a portion of the skin to separate into individual fibres.

[0011] Preferably the bast skin is decorticated bast skin.

[0012] Preferably the bast skin is in the form of fibre bundles.

DETAILED DESCRIPTION OF THE INVENTION

[0013] The method of the first aspect may be achieved by takingadvantage of the presence of enzyme-producing microorganisms that occurnaturally in green bast fibre. In particular, we have found that thisnatural retting of the decorticated hemp fibre can be achieved bymaintaining green decorticated hemp fibre under anaerobic condition fora predetermined period of time.

[0014] Accordingly, in a second aspect, the present invention provides amethod for separating bast skin into individual fibres, comprisingmaintaining fresh decorticated green bast skin in a closed containerunder anaerobic conditions for a period sufficient for at least aportion of the skin to separate into individual fibres.

[0015] Preferably the bast skin is decorticated bast skin comprisingfibre bundles.

[0016] The required anaerobic conditions may be established as a resultof production of gas(es) by the freshly decorticated green skin.Alternatively, or in addition, a non-oxygen gas may be introduced intothe container (eg nitrogen).

[0017] In the method of the second step, the natural enzymes alreadypresent in the green bast fibre may be augmented by one or more otherenzymes and/or chemical retting agent. They may be applied to the greenbast skins in any suitable manner, for example by soaking the skins inthe a composition containing the agent or by spraying a composition ontothe skins.

[0018] Alternatively, the method of the first aspect may be carried outby contacting dry decorticated bast skin with one or more enzymaticand/or chemical retting agent(s).

[0019] Accordingly, in a third aspect, the present invention provides amethod for separating bast skin into individual fibres, comprisingcontacting dry bast skin with at least one enzymatic and/or chemicalretting agent and incubating the bast skin in a closed container for aperiod sufficient for at least a portion of the bast skin to separateinto individual fibres.

[0020] Preferably, the bast skin is decorticated bast skin comprisingfibre bundles.

[0021] Preferably, in the method of the third aspect, the dry bast skinis contacted with the enzyme and/or chemical retting agent by soakingthe skin in a solution of the agent(s) and draining the skin beforeplacing it in the container.

[0022] The enzymatic and chemical retting agents may be those known inthe art. Examples of suitable enzymatic and chemical retting agentsinclude pectinases eg “Crystalzyme”, “Flaxzym”, Caustic, Soda ash,Sodium Silicate, Oxalic Acid, and EDTA.

[0023] The degree of degumming can be altered by changing the durationof degumming and/or the enzyme concentration. The concentration of theenzyme may be in the range of about 0.1 to about 2% (w/v), depending onthe required fibre fineness, the enzymes used for retting, and othertreatment conditions such as temperature and time.

[0024] The residence time of incubation and the enzyme concentration canbe selected to achieve the desired quality of the resultant fibres.

[0025] The bast skin used in the method of the invention may be obtainedby decorticating any bast plant. The bast plant may be ramie, flax andhemp. Preferably, the bast plant is hemp.

[0026] The term “bast skin” as used herein refers to the fibrous skin orrind that has been removed from the bast plant, for example bast skinthat is produced when a bast plant is subjected to decortication.

[0027] The bast skin may be that produced by any mechanicaldecortication process. Preferably, the skin is that produced by thedecortication process described in International Patent Application Nos.PCT/AU97/00329 and PCT/AU99/00858, the entire disclosures of which areincorporated herein by reference.

[0028] The substantially gas impervious container may be in the form ofa bag or the like into which decorticated skins may be placed. The bagmay be formed from any substantially gas impervious material. Thematerial may be a natural or synthetic plastic. Preferably the plasticis a flexible plastic.

[0029] The container may be formed from a gas pervious material that hasbeen treated to make it substantially gas impervious. The container maybe flexible, semi-rigid or rigid or a combination thereof. For examplethe container may be formed from paper, which has been treated to makeit substantially gas impervious, eg by forming a multilayer material alayer of which is substantially gas impervious.

[0030] The method of the present invention may be carried out undercontrolled temperature conditions. The controlled temperature(s) may bein the range of about 25° C. to about 55° C., with the optimumtemperature being dependent upon the specific enzymes used for retting.

[0031] Alternatively the method may be carried out under uncontrolledtemperature conditions. For example, the freshly decorticated greenskins may be placed into plastic bags or the like, the bags sealed andleft in the open (eg in a field) for a predetermined period.

[0032] The predetermined period is selected to obtain the desired amountof fibre separation and the quality of the final fibre. The period isdetermined by such factors the nature, type and/or characteristics ofthe bast fibre being treated, and the temperature(s) at which the methodis carried out.

[0033] Preferably, fibres treated in accordance with the method of theinvention are contacted (eg dunked) with hot water (eg about 70-90° C.),preferably followed by several times (eg 2 to 4 times) dunking in eitherhot or cold water. We have found that this squeezing improves the fibrefineness. The dunking and squeezing simulate the actions on aconventional wool scouring machine.

[0034] Accordingly, in a fourth aspect, the present invention provides amethod according to any one of the first to third aspects of theinvention comprising contacting the treated fibre with aqueous media andcompressing the fibre.

[0035] The aqueous media may be water.

[0036] Preferably, the compressing step involves combined rolling andcompressing of the fibres. The compressing step may involve pressureroller compression (squeezing) of the fibres.

[0037] The elevated temperature may be in the range of about 70 to 90°C. in the first hot water dunking.

[0038] In fifth aspect, the present invention provides a fibre productproduced by the method of the present invention.

[0039] We have found that the degree the level of degumming may beevaluated using a commercial Optical Fibre Diameter Analyser (OFDA). Thedegree of degumming can be assessed by measuring the width of degummedand opened fibres. This provides a speedy means of evaluating the degreeof fibre separating during degumming, even though the fineness of hempis not usually expressed in terms of fibre diameter or width. It ispossible to establish a correlation between this evaluation techniqueand conventional techniques of measuring the residual gum content andfibre linear density.

[0040] Accordingly, in yet a sixth aspect, the present inventionprovides a method for determining the degree of degumming of a rettedbast fibre product, comprising determining fibre width using an opticalfibre diameter measuring means.

[0041] We have found that the fibres of the present invention may bespun into yam or the like using conventional cotton spinning apparatuseg ring spinning, and rotor spinning. We have also found that byappropriate manipulation of the parameters of the fibre, they may beused in conventional wool spinning operations.

[0042] Prior to spinning, the fibre bundles produced by the process ofthe invention may be subjected to opening (eg using an opener) toseparate and open up the fibre. The opened fibre can then be subjectedto one or more carding operations.

[0043] Thus, in a seventh aspect, the present invention provides amethod according to any one of the first to third aspects of theinvention, comprising the additional steps of subjecting the fibre to atleast one opening operation followed by at least one carding operation.

[0044] The opening and carding operations are conventional (eg thoseused for cotton) and will be known to those skilled in the art.

[0045] The fibres produced by the method of the seventh aspect may rangefrom about 15 microns to about 30 microns. We have found that it ispossible to achieve very fine fibre diameters, for example 7 to 13micron. The invention extends to such fibres.

[0046] In a eighth aspect, the present invention provides a spun yarnformed by spinning bast fibres in accordance with the present invention.

[0047] Preferably, the bast fibre is hemp fibre. The yarn of the eighthaspect may be a blend of a fibre in accordance with invention with oneor more other fibres.

[0048] In an ninth aspect, the present invention provides a fabric ormaterial manufactures from fibre in accordance with the presentinvention.

[0049] In order that the present invention may be more readilyunderstood, we provide the following non-limiting embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0050]FIG. 1 shows a flow chart of the procedures involved in degummingand evaluating the hemp fibres;

[0051]FIG. 2 is a graph showing the effect of incubation time on fibrewidth; and

[0052]FIG. 3 is a graph showing the effect of enzyme concentration onfibre width.

EMBODIMENTS OF THE INVENTION

[0053] Referring to FIG. 1, the raw material can be either decorticateddry skin or decorticated green skin. If decorticated dry bast fibres areto be used, the skins are soaked in an enzyme solution first for about 5minutes, this is following by draining, for about 2 minutes, thesolution from the soaked skins to reduce the liquor ratio.

[0054] After draining, the skins are sealed in a container (eg plasticbag) and incubated for a pre-determined period of time. Hot waterdunking of the bast fibres follows the incubation order to stop furtherenzyme action. This is then followed by pressure roller squeezing, plusfurther dunking and squeezing to improve the fibre cleanness andfineness.

[0055] To evaluate the textile attributes of the treated fibres, thefibres are oiled and dried, opened gradually, conditioned under standardtest conditions and tested for fibre fineness (expressed in fibre widthhere) on an optical fibre diameter analyser (OFDA).

[0056] If decorticated green skins are to be used as the startingmaterial, the skins can be sealed in a container (eg plastic bag)directly, or after being sprayed with an enzyme solution to enhance theretting performance. The remaining steps are the same as described inthe previous paragraph for the decorticated dry skins.

TEST RESULTS

[0057] Dry skin

[0058] Decorticated and dry skins of the Ukraine variety (Zolotonshka)were mixed and prepared in batches of 800 grams for the evaluationexperimentation. The chemicals used were:

[0059] Enzymes:

[0060] 0.1% (w/v)→1 g/L (Crystalzyme from Enzyme solutions P/L) Higherenzyme concentrations were also used

[0061] Oxalic acid: 50 milli mole→6.3 g/L (Oxalic acid in the form of(COOH)₂*2(H₂O ))

[0062] Wetting agent: Cibaflow CIR→0.5 g/L

[0063] Solution: 10 Litres

[0064] The incubation conditions were:

[0065] Temperature: 50° C. degrees

[0066] pH value: 3.5 (buffered with Sodium Acetate to 3.25 first; SodiumAcetate in the form of NaC₂H₃O₂ 3(H₂O) at 8.3 g/L)

[0067] Duration: 4, 6, 8, 10, 24 hours

[0068] The procedures as outlined in FIG. 1 for the dry skin werefollowed. Table 1 gives a summary of the trial conditions and results.The results are also plotted in FIGS. 2 and 3 to show the effects ofincubation time and enzyme concentration on the fibre fineness results.TABLE 1 Experimental details Incubation Enzyme — Average periodCrystalzyme/ Fibre Fineness Batch No (hours) Oxalic acid Micron Batch 14 0.1%/ 31.14 50 mmole Batch 2 6 0.1%/ 30.71 50 mmole Batch 3 8 0.1%/29.96 50 mmole Batch 4 10 0.1%/ 30.49 50 mmole Batch 5 24 0.1%/ 29.20 50mmole Batch 6 4 0.3%/ 29.21 50 mmole Batch 7 4 0.5%/ 28.96 50 mmole

[0069] Green Skin

[0070] Green hemp skins were kept in a sealed plastic bag for about aweek to allow natural retting to occur under anaerobic conditions. Afterfibre opening and sample carding, the width of the degummed fibres wasmeasured on the Optical Fibre Diameter Analyser, and the average widthis about 22.5 microns.

[0071] Any discussion of documents, acts, materials, devices, articlesor the like which has been included in the present specification issolely for the purpose of providing a context for the present invention.It is not to be taken as an admission that any or all of these mattersform part of the prior art base or were common general knowledge in thefield relevant to the present invention as it existed before thepriority date of each claim of this application.

[0072] It will be appreciated by persons skilled in the art thatnumerous variations and/or modifications may be made to the invention asshown in the specific embodiments without departing from the spirit orscope of the invention as broadly described. The present embodimentsare, therefore, to be considered in all respects as illustrative and notrestrictive.

1. A method for separating decorticated bast skin into individualfibres, comprising maintaining decorticated bast skin in a closedcontainer in the presence of at least one enzymatic and/or chemicalretting agent for a period sufficient for at least a portion of the skinto separate into individual fibres.
 2. A method according to claim 1,wherein the bast skin is decorticated bast skin comprising fibrebundles.
 3. A method according to claim 1 or claim 2, wherein the bastskin comprises at least in part fresh green bast skin and the at leastone enzymatic retting agent is a naturally occurring enzyme of the greenbast skin.
 4. A method according to any one of the previous claims claim1, wherein the bast skin is maintained under anaerobic conditions for aperiod sufficient for at least a portion of the bast skin to separateinto individual fibres.
 5. A method according to claim 4, wherein theanaerobic conditions are established at least in part by the productionof gas(es) by the fresh green skin.
 6. A method according to any one ofclaim 3 to 5 claim 3, wherein the naturally occurring enzyme isaugmented by at least one other enzymatic or chemical retting agent or acombination thereof.
 7. A method according to claim 1 or claim 2,wherein the bast skin is substantially dry bast skin.
 8. A methodaccording to claim 7, wherein the bast skin is contacted with at leastone enzymatic and/or chemical retting agent(s).
 9. A method according toany one of the preoeding claims claim 1, wherein the bast skin iscontacted with the enzyme and/or chemical retting agent by soaking theskin in a solution of the agent(s) and draining the skin before placingit in the container.
 10. A method according to any one of the precedingclaims claim 1, wherein the enzymatic or chemical retting agent(s)is/are selected from the group consisting of Crystalzyme. Flaxzym,Caustic, Soda ash and Sodium Silicate, Oxalic Acid, and EDTA.
 11. Amethod according to any one of the preceding claims claim 1, wherein theconcentration of the enzyme solution contacted with the bast skin is inthe range of about 0.1 to about 2% (w/v).
 12. A according to any one ofthe preceding claims claim 1, wherein the separation is carried out at atemperature in range of about 25° C. to about 55° C.
 13. A methodaccording to any one of the precedind claims claim 1, wherein the bastskin is derived from a bast plant selected from the group consisting oframie, flax and hemp.
 14. A method according to any one of the precedingclaims claim 1, wherein the bast skin is derived from hemp.
 15. A methodaccording to any one of the preceding claims claim 1, wherein the closedcontainer is a substantially gas impervious container.
 16. A methodaccording to claim 15, wherein the substantially gas imperviouscontainer is in the form of a bag or the like into which decorticatedskins may be placed.
 17. A method according to claim 16, wherein the bagis formed at least in part from a natural or synthetic plastic.
 18. Amethod according to claim 17, wherein the plastic is a flexible plastic.19. A method according to any one of the 1 to 17 claim 1, wherein thecontainer is formed from a gas-pervious material which has been treatedto make it substantially gas impervious.
 20. A method according to anyone of the previous claims claim 1 when carried out under controlledtemperature conditions.
 21. A method according to any one of claim 1 to18 claim 1, carried out under uncontrolled temperature conditions.
 22. Amethod according to any one of claim 21, wherein the contained bastskins are left in the open for a predetermined period.
 23. A methodaccording to any one of the preceding claimsclaim 1, further comprisingcontacting the bast skins with hot water.
 24. A method according toclaim 23, wherein the hot water treated fibres are contacted at leastone time with either hot or cold water.
 25. A method according to claim23 or 24, wherein the fibres are subjected to a squeezing to remove aleast part of liquid therefrom.
 26. A method according to any one ofclaim 1to 23 claim 1, further including the step of contacting thetreated fibre with aqueous media and compressing the fibre.
 27. A methodaccording to claim 25, wherein the treated fibres are subjected to aleast 2 aqueous media contacting steps.
 28. A method according to claims26 or claim 27, wherein the aqueous media is water.
 29. A methodaccording to any one of claims 26 to 28 claim 26, wherein thecompressing step involves combined rolling and compressing of thefibres.
 30. A method according to claim 29, wherein the compressing stepinvolves pressure roller compression (squeezing) of the fibres.
 31. Amethod according to any one of claims 26 to 30 claim 26 wherein thefibre is contacted with the aqueous media at elevated temperature.
 32. Amethod according to claim 31, wherein the elevated temperature is in therange of about 70 to 90° C.
 33. A method according to claim 31 or claim32, wherein the fibre is contacted with the aqueous media by dunking thefibre in the aqueous media.
 34. A fibre produced by a method accordingto any one of the preceding claims claim
 1. 35. A fibre according toclaim 34, which has been subjected to an opening operation.
 36. A fibreaccording to any one of claims 34 to 35 claim 34 which has beensubjected to a carding operation.
 37. Yarn comprising a fibre accordingto any one of claims 34 to 36 claim
 34. 38. A fabric or materialcomprising a fibre in accordance with any one of claims 34 to 37 claim34.
 39. A method for separating bast skin into individual fibres,comprising maintaining bast skin under anaerobic conditions in thepresence of at least one enzymatic and/or chemical retting agent for aperiod sufficient for at least a portion of the skin to separate intoindividual fibres.
 40. A method for determining the degree of degummingof a retted bast fibre product, comprising determining fibre width ofthe retted bast fibre using an optical fibre diameter measuring means.